Cations: Definition & Examples

Cations: Definition & Examples
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  • 0:00 What Is a Cation?
  • 1:38 Identifying Atoms That…
  • 1:58 How Cations Are Formed
  • 3:27 Cations Interacting…
  • 3:53 Importance of Cations
  • 5:19 Lesson Summary
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Lesson Transcript
Instructor: Cynthia Shonberg

Cynthia has taught high school science courses for many years and has a Master of Science degree and a Master of Arts in Teaching.

In this lesson, you will learn that cations are positively charged atoms, and you will discover how they are formed. You will also become familiar with some common cations, and you should be able to determine which atoms form cations.

What Is a Cation?

What do a battery, your heart, and fertile soil have in common? Answer: All of these require cations in order to work.

But let's get a little more specific. Have you ever gulped down a sports drink after becoming dehydrated from physical activity? Maybe a trainer, gym teacher, or even a sports drink commercial told you that consuming the beverage would help you replace your electrolytes. An electrolyte is a solution that contains ions. And in drinking that sports drink, you have consumed cations. But what is a cation?

A cation is a positively charged atom. As you may know, an atom is electrically neutral. This is because the number of protons and the number of electrons in an atom are equal, and the charges balance out. When an atom forms a cation by losing one or more electrons, it now has more protons, or positively charged particles, than electrons, or negatively charged particles.

Here, you can see all this in action. When sodium loses an electron, the resulting cation has a +1 net positive charge. Similarly, when calcium loses 2 electrons, the resulting cation has a +2 net positive charge.

Examples of net charges

It's helpful to know that an atom can form a negatively charged ion by gaining one or more electrons, and these are known as anions. One way to remember the difference between a cation and an anion is to say to yourself, 'I positively love cats!'

Identifying Atoms That Form Cations

As mentioned above, a cation is formed from an atom when the atom loses one or more electrons. Elements that are metals form cations. In the periodic table, note that the metallic elements are in Group I, Group II and in Groups III-XII, the transition metals.

Periodic Table of Elements

How Cations Are Formed

So why do atoms lose electrons in the first place? As you may know from previous learning about atomic structure, the electrons of atoms are located in electron shells, or orbitals. When atoms have fewer than 8 electrons in their outermost shells, they tend to form chemical bonds by losing, gaining or sharing electrons.

The atoms in Group I of the periodic table have one electron in their outermost electron shell. In order to fulfill the octet rule, atoms in this group will give away the outer shell electron to a nonmetal atom that has 7 electrons in its outermost shell. The octet rule states that atoms are most stable when they contain 8 electrons in their outermost shell.

When electrons are lost from the outermost shell, the outermost shell is also lost. The result is that the shell inside of the outer one becomes the new outermost shell, and it contains 8 electrons. The atom is now stable.

Cation Formation

Atoms in Group II have 2 electrons in their outermost shell and will form bonds with atoms that have 6 electrons in their outermost shells, or with 2 atoms that have one electron each in their outermost shell. For example, road salt, calcium chloride, forms from one calcium atom bonding with 2 atoms of chlorine.

Note that very small atoms, such as hydrogen and lithium, are stable when their outermost electron shells contain 2 electrons.

Cations Interacting With Anions

Cations and anions form ionic bonds because of the attraction between them. A positively charged cation is attracted to a negatively charged anion because opposites attract.

The image below shows how a cation and an anion interact to form an ionic bond. Table salt, NaCl, is formed when sodium gives away its outermost electron to chlorine.

Ionic Bonding

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